Composition for a tire tread and process for its preparation

ABSTRACT

The present invention relates to a cross-linkable or cross-linked rubber composition having improved hysteresis properties in the cross-linked state which is useful for the manufacture of treads for tires. The rubber composition of the present invention comprises at least one diene elastomer having a molar ratio of units originating from conjugated dienes which is greater than 30% and comprising carboxylic acid functions along its chain, and a reinforcing inorganic filler. The present invention further relates to a process for preparing such a cross-linkable or cross-linked rubber composition as well as to a tire having reduced rolling resistance and a tread for a tire where the tread comprises the rubber composition of the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application NumberPCT/EP01/05802, published in French on Nov. 29, 2001 as InternationalPublication Number WO 01/90237 A1 and filed on May 21, 2001, whichclaims priority to French Patent Application Number 00/06597, filed onMay 22, 2000.

FIELD OF THE INVENTION

The present invention relates to a cross-linkable or cross-linked rubbercomposition having improved hysteresis properties in the cross-linkedstate, which is usable to constitute a tire tread or to be used therein.The present invention further relates to a process for the preparationof such a cross-linkable rubber composition, to a tread comprising thecross-linked rubber composition, and to a tire having reduced rollingresistance.

BACKGROUND OF THE INVENTION

Since fuel economies and the need to preserve the environment havebecome priorities, it has become desirable to produce mixes having goodmechanical properties and as low a hysteresis as possible so that theycan be processed in the form of rubber compositions useful for themanufacture of various semi-finished products involved in the make-up oftires, including, for example, underlayers, sidewalls or treads. It isalso desirable to obtain tires having reduced rolling resistance.

To achieve such objectives, numerous solutions have been proposed,consisting of, in particular, the modification of the structure of dienepolymers and copolymers at the end of polymerization by means offunctionalizing, coupling or starring agents. The great majority ofthese solutions have focused on the use of functionalized polymers,which are active with respect to carbon black, with the goal ofobtaining a good interaction between the modified polymer and the carbonblack.

By way of illustrating the prior art relating to reinforcing fillersformed of carbon black, mention may be made of U.S. Pat. No. 3,135,716,which describes the reaction of living diene polymers at the end of achain with a polyfunctional organic coupling agent in order to obtainpolymers having improved properties. Mention may also be made of U.S.Pat. No. 3,244,664, which discloses the use of tetra-alkoxysilanes as acoupling agent or starring agent for diene polymers.

Silica has been used as a reinforcing filler in cross-linkable rubbercompositions, in particular those compositions intended for use in tiretreads, for a long time. However, this use has remained very limitedbecause of the unsatisfactory level of certain physical properties ofsuch compositions, in particular, abrasion resistance.

Thus, it has been proposed, in order to overcome these drawbacks, to usefunctionalized diene polymers, instead of the non-functionalizedpolymers which were used before, and in particular polymersfunctionalized by alkoxysilane derivatives, such as tetraethoxysilanes.For example, mention may be made of U.S. Pat. No. 5,066,721, whichdescribes a rubber composition comprising a diene polymer functionalizedby an alkoxysilane having at least one non-hydrolyzable alkoxyl radical,which makes it possible to eliminate the polymerization solvent by steamstripping.

One disadvantage of these functionalization reactions lies in thecoupling reactions which accompany them, which generally make itnecessary to use an excess of alkoxysilane and/or to employ intensivemixing, in order to minimize these coupling reactions.

Another drawback of these reactions lies in the later implementation ofthe steam stripping operation, which is necessary to eliminate thepolymerization solvent. In fact, generally, experience shows that thefunctionalized polymers obtained undergo changes in macrostructureduring this stripping operation, which result in serious degradation oftheir properties, unless one is limited to using as the functionalizingagent an alkoxysilane belonging to a restricted family, such as thatdescribed in the aforementioned U.S. Pat. No. 5,066,721.

Consequently, it may be seen from the above that the use of dienepolymers comprising an alkoxysilane function to obtain rubbercompositions comprising silica as reinforcing filler is notsatisfactory, despite the improved physical properties of thesecompositions.

Thus, research has been conducted on other functionalization reactions,always with a view to obtaining such rubber compositions.

By way of example, mention may be made of French Patent No. FR2.740.778, assigned to the Assignee of the present invention, whichdiscloses the incorporation, into rubber compositions that comprise, asthe reinforcing filler, silica in a majority proportion (for example, ablend of silica and carbon black), of diene polymers bearing at thechain end a silanol function or a polysiloxane block having a silanolend. For example, a functionalizing agent consisting of a cyclicpolysiloxane, such as hexamethylcyclotrisiloxane, may be used. Thefunctionalized polymers obtained can be separated from the reactionmedium, resulting in their formation by steam extraction of the solvent,without their macrostructure and consequently their physical propertieschanging.

Mention may also be made of European Patent No. EP 0 877 047, whichdiscloses the incorporation of such polymers having a silanol functionin rubber compositions comprising as the reinforcing filler carbon blackhaving silica fixed to its surface.

It has been possible to establish that these polymers impart rubberproperties, in particular, hysteresis and reinforcement properties, inthe cross-linked state, which are improved compared with those ofcontrol compositions based on non-functionalized diene polymers, andwhich are at least analogous to those of compositions based on dienepolymers comprising an alkoxysilane function.

Mention may also be made of European Patent No. EP 0 692 493, whichestablishes that diene polymers bearing at the chain end alkoxysilanegroups and an epoxy group result in improved reinforcement propertiesand in reduced hysteresis losses at small and large deformations.

One disadvantage of these polymers, which comprise a functional groupthat is active for coupling to silica or to carbon blacksurface-modified by silica, is that the improvement in the hysteresisand reinforcement properties which they impart to the rubbercompositions incorporating them is generally accompanied by a processingability of the non-cross-linked mixes which is compromised when comparedto the processing ability of non-functionalized “control” polymers.

Among the other functionalization reactions studied, mention may bemade, for example, of the functionalization of the diene polymers alongthe chain by COOH functions.

The functionalization along the chain can be effected by directmetallation, in the presence of N,N,N′,N′-tetramethylethylenediamine(TMED), by means of butyllithium or metallic sodium (as described inU.S. Pat. Nos. 3,978,161 and 3,976,628, respectively), followed by acarbonation reaction by means of carbonic gas. However, such a processhas the disadvantage of generally resulting in cuts in the chain of themodified polymer.

Two specific reagents, of the respective formulae HSCH₂CO₂CH₃ andN₂CHCO₂CH₂CH₃, have also been used to graft COOH functions along thechain of a diene polymer. For the description of the reaction mechanismsrelating to the use of these two reagents, reference may be maderespectively to the following documents: Sanui et al., J. Poly. Sci.,Polym. Chem. Ed. 12:1965 (1974) and Tanaka et al., J. Poly. Sci., Polym.Chem. Ed. 17:2975 (1979). However, one major disadvantage of using oneor the other of these two reagents is that it results in significantchanges in macrostructure for the modified polymer.

This functionalization along the chain may also be implemented by meansof carbon monoxide, either by hydroformylation followed by oxidation ofthe aldehyde formed (as described in U.S. Pat. No. 4,912,145), or bydirect hydrocarboxylation of the polymer (as described in Ajjou et al.,Macromolecules 29:1784 (1996)). The catalysts used for these reactionsare based on rhodium or palladium. One disadvantage of thisfunctionalization by carbon monoxide lies, on one hand, in the drasticnature of the operating conditions and, on the other hand, in thefrequent formation of a gel in the reaction medium.

Functionalization by means of maleic anhydride is more widespread. Thistype of functionalization makes it possible to obtain succinic anhydrideunits along the chain, which are precursors of the COOH functions.Reference may be made to U.S. Pat. Nos. 4,082,817 and 4,082,493 forexamples of implementation of such functionalization. However, thismethod of functionalization may also result in the formation of a gel.

The use of diene elastomers comprising COOH functions along the chainfor the preparation of rubber compositions useful in tires, isdisclosed, in particular, by U.S. Pat. No. 5,494,091. This documentdiscloses a rubber composition filled with carbon black comprising 25 to55 phr (where phr represents parts by weight per hundred parts ofelastomeric matrix) of polyisoprene and 45 to 75 phr of a diene polymerbelonging to the group consisting of homopolymers of conjugated dienesand copolymers of conjugated dienes with mono-olefins, such as EPDMterpolymers (of ethylene, propylene and a diene), where part of at leastone of these polymers comprises COOH functions grafted along the chainby reaction with a metal salt of unsaturated carboxylic acid, forexample zinc dimethacrylate. The composition thus obtained is supposedto have a sufficiently high rigidity to be used in an internalreinforcement rubber for tire sidewalls, so as to permit travel with aflat tire under satisfactory conditions.

SUMMARY OF THE INVENTION

The present invention relates to the unexpected discovery of across-linkable or cross-linked rubber composition having reducedhysteresis losses at small and large deformations, which are similar tothose hysteresis losses of known compositions based on polymerscomprising functional groups which are active for coupling to silica(such as the alkoxysilane or silanol groups mentioned above). Thecross-linkable or cross-linked rubber composition of the presentinvention also has processing properties in the non-cross-linked statewhich are improved compared with the processing properties of knowncompositions filled with silica. The processing properties of the rubbercomposition of the present invention are also comparable to theprocessing properties of compositions based on non-functionalizedpolymers that are filled with silica.

The cross-linkable or cross-linked rubber composition of the presentinvention is obtained by the association of at least one diene elastomerhaving a molar ratio of units originating from conjugated dienes greaterthan 30% and comprising carboxylic acid functions along its chain with areinforcing inorganic filler.

The advantageous characteristics of the rubber composition of thepresent invention make such a composition useful to constitute a treadfor a tire. Thus, the present invention further relates to a tire and atread for a tire comprising or made of the rubber composition of thepresent invention. The present invention also relates to a process forforming the rubber composition of the present invention, described inmore detail below.

DETAILED DESCRIPTION OF THE INVENTION

In the rubber compositions of the present invention, certain dieneelastomers, such as butyl rubbers, nitrile rubbers or copolymers ofdienes and alpha-olefins of the EPDM type, for example, cannot be usedin the compositions according to the invention because of their reducedcontent of units of diene origin, which makes the correspondingcompositions unsuitable for use in making tire treads.

In certain preferred embodiments, the diene elastomer of the compositionaccording to the present invention is a “highly unsaturated” dieneelastomer, meaning a diene elastomer having a content of units of dieneorigin (conjugated dienes) which is greater than 50%.

The following may be used as the diene elastomer in the compositionsaccording to the present invention: (1) a homopolymer obtained bypolymerization of a conjugated diene monomer having 4 to 12 carbonatoms; or (2) a copolymer obtained by copolymerization of one or moredienes conjugated together or with one or more vinyl-aromatic compoundshaving 8 to 20 carbon atoms.

The diene elastomer used in the compositions according to the presentinvention may be prepared anionically or by any other method, providedthat it has the aforementioned characteristics. Mention may be made, forexample, of synthesis by radical polymerization effected in emulsion,which is known to give polymers having COOH functions along the chainand which is described, in particular, in Lovell et al., EmulsionPolymerization and Emulsion Polymers, John Wiley & Sons, pp. 558-561(1997) and in the references cited therein.

Suitable conjugated dienes include, in particular: 1,3-butadiene;2-methyl-1,3-butadiene; 2,3-di(C1 to C5 alkyl)-1,3-butadienes, such as2,3-dimethyl-1,3-butadiene or 2,3-diethyl-1,3-butadiene;2-methyl-3-ethyl-1,3-butadiene; 2-methyl-3-isopropyl-1,3-butadiene; anaryl-1,3-butadiene; 1,3-pentadiene; and 2,4-hexadiene.

Suitable vinyl-aromatic compounds include, for example: styrene; ortho-,meta- and para-methylstyrene; the commercial mixture “vinyltoluene”;para-tert. butylstyrene; methoxystyrenes; chlorostyrenes;vinylmesitylene; divinylbenzene; and vinylnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene unitsand between 1% and 80% by weight of vinyl-aromatic units. The elastomersmay have any microstructure, which is a function of the polymerizationconditions used, in particular of the presence or absence of a modifyingand/or randomizing agent and the quantities of modifying and/orrandomizing agent used. The elastomers may, for example, be block,statistical, sequential or microsequential elastomers, and may beprepared in dispersion or in solution. They may be coupled and/orstarred or alternatively functionalized with a coupling and/or starringor functionalizing agent.

Polybutadienes are preferred, in particular those having a content of1,2-units of between 4% and 80%, or those having a content of cis-1,4bonds of more than 80%; synthetic polyisoprenes; butadiene-styrenecopolymers, in particular those having a styrene content of between 5%and 50% by weight and, more particularly, between 20% and 40%, a contentof 1,2-bonds of the butadiene fraction of between 4% and 65%, and acontent of trans-1,4 bonds of between 20% and 80%; butadiene-isoprenecopolymers, in particular those having an isoprene content of between 5%and 90% by weight and a glass transition temperature (T_(g)) of between−40° C. and −80° C.; isoprene-styrene copolymers, in particular thosehaving a styrene content of between 5% and 50% by weight and a T_(g) ofbetween −25° C. and −50° C.

In the case of butadiene-styrene-isoprene copolymers, those which aresuitable are, in particular, those having a styrene content of between5% and 50% by weight and, more particularly, between 10% and 40%, anisoprene content of between 15% and 60% by weight, and more particularlybetween 20% and 50%, a butadiene content of between 5% and 50% byweight, and more particularly between 20% and 40%, a content of1,2-units of the butadiene fraction of between 4% and 85%, a content oftrans-1,4 units of the butadiene fraction of between 6% and 80%, acontent of 1,2-plus 3,4-units of the isoprene fraction of between 5% and70%, and a content of trans-1,4 units of the isoprene fraction ofbetween 10% and 50%, and more generally any butadiene-styrene-isoprenecopolymer having a T_(g) of between −20° C. and −70° C.

In particularly preferred embodiments, the diene elastomer of thecomposition according to the present invention is selected from thegroup of highly unsaturated diene elastomers consisting ofpolybutadienes (BR), synthetic polyisoprenes (IR), butadiene-styrenecopolymers (SBR), butadiene-isoprene copolymers (BIR), isoprene-styrenecopolymers (SIR), butadiene-styrene-isoprene copolymers (SBIR), andmixtures of two or more of these compounds.

Even more preferably, the diene elastomer is selected from the groupconsisting of polybutadienes, butadiene-styrene copolymers andbutadiene-styrene-isoprene copolymers.

According to a preferred embodiment of the invention, the dieneelastomer used is a butadiene-styrene copolymer prepared in solutionhaving a styrene content of between 20% and 30% by weight, a content ofvinyl bonds of the butadiene fraction of between 15% and 65%, a contentof trans-1,4 bonds of between 15% and 75% and a T_(g) of between −20° C.and −55° C.

According to another preferred embodiment of the present invention, thediene elastomer used is a butadiene-styrene copolymer prepared inemulsion, preferably having a total quantity of emulsifier which is lessthan 3.5 phr (phr: parts by weight per hundred parts of elastomer).

In the present invention, the aforementioned diene elastomers useful inthe present compositions may be obtained from any anionic initiator(whether it be monofunctional or polyfunctional) or a non-anionicinitiator. However, preferably, an anionic initiator containing analkali metal such as lithium, or an alkaline-earth metal such as bariumis used.

Suitable organolithium initiators include, in particular, thosecomprising one or more carbon-lithium bonds. Mention may be made, forexample, of aliphatic organolithiums, such as ethyllithium,n-butyllithium (nBuLi), isobutyllithium, and dilithium polymethylenes,such as 1-4 dilithiobutane. Lithium amides, which are obtained from anacyclic or cyclic secondary amine, such as pyrrolidine orhexamethyleneimine, may also be used.

Also, diene elastomers useful in the present invention include dieneelastomers which are initiated by compounds of transition metals, suchas compounds of titanium for example, or by rare earths, such asneodymium.

The polymerization, as is known to a person skilled in the art, ispreferably effected in the presence of an inert solvent, which may be,for example, an aliphatic or alicyclic hydrocarbon such as pentane,hexane, iso-octane, cyclohexane, methylcyclohexane, cyclopentane, or anaromatic hydrocarbon such as benzene, toluene or xylene. Thispolymerization may be effected continuously or discontinuously. It isgenerally effected at a temperature of between 20° C. and 120° C.,preferably between 30° C. and 100° C.

The functionalization of the diene elastomers, obtained by COOHfunctions along the chain, may advantageously be effected according tothe process described in French Patent Application Serial No. 99/05746(assigned to the Assignee of the present invention), which relatesgenerally to the functionalization of any polymers comprising at leastone double bond, for example polymers obtained from monomers such asisoprene, butadiene, isobutylene, a vinyl-aromatic compound orterpolymers of ethylene, propylene and a diene.

This process comprises: (1) a first step, wherein the starting polymeris subjected to a hydroalumination or carboalumination reaction alongits chain in an inert hydrocarbon solvent, by the addition of an agentderived from aluminum to the starting polymer; (2) a second step ofadding to the product of the reaction of the first step at least oneelectrophilic agent intended to react with the agent derived fromaluminum; and (3) a third step of later stopping the functionalizationreaction of the second step and recovering the polymer functionalizedalong its chain.

The hydroalumination or carboalumination reactions of the first step ofthe process involve the addition of an Al—H or an Al—C bond,respectively, to a double bond of the starting polymer in accordancewith the reactions Al—H+C═C→H—C—C—Al or Al—C+C═C→C—C—C—Al, respectively.In order to implement these reactions, in particular, an alkyl aluminumor an aluminate may be used as the agent derived from aluminum. Inpreferred embodiments, diisobutyl aluminum hydride is used.

This first step is advantageously implemented in an inert hydrocarbonsolvent, such that the number of moles of the agent derived fromaluminum per 1000 grams of starting polymer is between 0.05 and 5 moles,and preferably between 0.05 and 0.5 mole. In particular, toluene,xylene, heptane, or cyclohexane may be used as the inert hydrocarbonsolvent. Preferably, this first step is implemented at a temperature ofbetween 20° C. and 100° C. and, even more preferably, between 50° C. and70° C.

To implement the second step of the process, anhydrides, in particular,carbon dioxide, are preferably used as the electrophilic agent to obtaina polymer having carboxylic acid functions along the chain. A cyclicanhydride may also be used, such as succinic anhydride. This second stepis advantageously implemented such that the molar ratio of the number ofmoles of electrophilic agent to the number of moles of agent derivedfrom aluminum is equal to or greater than 3. Preferably, this secondstep is implemented at a temperature of between 20° C. and 100° C. and,even more preferably, between 50° C. and 70° C.

For stopping the functionalization reaction of this second step, thereis preferably added a metallic complexing agent which also has theeffect of liquefying the reaction medium. This complexing agentpreferably comprises a metallic chelate capable of releasing at leastone proton during the complexing reaction. Preferably, acetylacetone isused as the chelate. Benzoyl acetone or 8-hydroxyquinoline may also beused. The molar ratio of the number of moles of the metallic complexingagent to the number of moles of agent derived from aluminum is thenequal to or greater than 3.

In the case of carboxylic acid functionalization where carbon dioxide isused as the electrophilic agent, following the addition of the metalliccomplexing agent, there is added to the reaction medium a highlyprotonic acid to finish the stopping of the functionalization. Thishighly protonic acid may be, for example, hydrochloric acid. The molarratio of the number of moles of highly protonic acid to the number ofmoles of agent derived from aluminum is then equal to or greater than 3.

For the carboxylic acid functionalization of a diene elastomer, such asa styrene-butadiene copolymer prepared in emulsion, there may be used asthe functionalizing agent an unsaturated aliphatic monocarboxylic ordicarboxylic acid, for example, acrylic acid, maleic acid or fumaricacid, or, alternatively, a carbocyclic carboxylic acid, such as cinnamicacid.

Of course, the compositions of the invention may contain a single dieneelastomer such as the aforementioned one or a mixture of several ofthese diene elastomers.

The diene elastomers according to the present invention, having COOHfunctions along the chain, may be used on their own in the compositionaccording to the invention, or may be used in a blend with any otherelastomer conventionally used in tires, such as natural rubber or ablend based on natural rubber and a synthetic elastomer, oralternatively another diene elastomer which may possibly be coupledand/or starred or alternatively partially or entirely functionalizedother than with COOH functions along the chain.

It will be noted that the improvements in the properties of the rubbercomposition according to the invention will be greater as the proportionof said conventional elastomer(s) is lower in the composition accordingto the invention. Advantageously, this or these conventionalelastomer(s) may be present in the composition according to theinvention, if applicable, in a quantity of from 1 to 70 parts by weightper 100 parts by weight of diene elastomer(s) according to the inventionhaving COOH functions along the chain.

In the present application, “reinforcing inorganic filler”, in a knownmanner, is understood to mean an inorganic or mineral filler, whateverits color and its origin (natural or synthetic), which may also bereferred to as a “white” filler or a “clear” filler, in contrast tocarbon black. This inorganic filler is capable, on its own, without anymeans other than an intermediate coupling agent, of reinforcing a rubbercomposition intended for the manufacture of tires. In other words, thisinorganic filler is capable of replacing a conventional tire-gradecarbon black filler in its reinforcement function.

Preferably, the reinforcing inorganic filler is present in thecomposition of the invention in a quantity equal to or greater than 40phr (phr: parts by weight per hundred parts of diene elastomer(s)). Alsopreferably, this reinforcing inorganic filler is present in a majorityproportion in the reinforcing filler of the composition of theinvention, such that its mass fraction in said reinforcing filler isgreater than 50%.

Advantageously, the entirety (or at the very least a majorityproportion) of said reinforcing inorganic filler is silica (SiO₂). Thesilica used may be any reinforcing silica known to the person skilled inthe art, in particular, any precipitated or pyrogenic silica having aBET surface area and a specific CTAB surface area both of which are lessthan 450 m²/g, even if the highly dispersible precipitated silicas arepreferred.

In the present specification, the BET specific surface area isdetermined in a known manner, in accordance with the method described inBrunauer et al., Journal of the American Chemical Society, vol. 60, page309 (February 1938) and corresponding to Standard AFNOR-NFT-45007(November 1987). The CTAB specific surface area is the external surfacearea determined in accordance with the same Standard AFNOR-NFT-45007 ofNovember 1987.

“Highly dispersible silica” is understood to mean any silica having asubstantial ability to disagglomerate and to disperse in an elastomericmatrix, which can be observed in known manner by electron or opticalmicroscopy on thin sections. Non-limiting examples of such preferredhighly dispersible silicas include: the silica Perkasil KS 430,commercially available from Akzo; the silica BV 3380, commerciallyavailable from Degussa; the silicas Zeosil 1165 MP and 1115 MP,commercially available from Rhodia; the silica Hi-Sil 2000, commerciallyavailable from PPG; the silicas Zeopol 8741 or 8745, commerciallyavailable from Huber; and treated precipitated silicas such as, forexample, the aluminum-“doped” silicas described in European Patent No.EP 0 735 088.

The physical state in which the reinforcing inorganic filler is presentis immaterial, whether it be in the form of a powder, microbeads,granules or balls. Of course, “reinforcing inorganic filler” is alsounderstood to mean mixtures of different reinforcing inorganic fillers,in particular of highly dispersible silicas such as those describedabove.

It will be noted that the reinforcing filler of a rubber compositionaccording to the present invention may contain carbon black in a blendor mixture, in addition to the aforementioned reinforcing inorganicfiller or fillers, in a minority proportion (that is to say, in a massfraction of less than 50%). Any carbon black may be suitable including,in particular, the blacks of the type HAF, ISAF and SAF, which areconventionally used in tires, and particularly in tire treads.Non-limiting examples of such blacks include the blacks N115, N134,N234, N339, N347 and N375.

For example, black/silica blends or blacks partially or integrallycovered with silica are suitable for forming the reinforcing filler.Also suitable are reinforcing inorganic fillers comprising carbon blacksmodified by silica such as, for example, the fillers sold by CABOT underthe name “CRX 2000”, which are described in International PatentPublication No. WO 96/37547.

The following may also be used, for example, as the reinforcinginorganic filler: aluminas (of the formula Al₂O₃), such as the aluminasof high dispersibility which are described in European Patent No. EP 0810 258; or aluminum hydroxides, such as those described inInternational Patent Publication No. WO 99/28376.

In embodiments where the reinforcing filler contains only a reinforcinginorganic filler and carbon black, the mass fraction of the carbon blackin the reinforcing filler preferably is less than or equal to 30%.

However, the aforementioned properties of the composition according tothe present invention are improved all the more, the higher the massfraction of reinforcing inorganic filler is in the reinforcing fillerwhich makes up part of the composition of the present invention. Theseproperties are optimal when the composition contains solely areinforcing inorganic filler, for example, silica, as the reinforcingfiller. Thus, it is preferred in certain embodiments of the presentinvention for the rubber composition to contain solely a reinforcinginorganic filler (for example, silica) as the reinforcing filler.

The rubber composition according to the invention also comprises, inconventional manner, a reinforcing inorganic filler/elastomeric matrixbonding agent (also referred to as coupling agent), the function ofwhich is to ensure sufficient chemical and/or physical bonding (orcoupling) between the inorganic filler and the elastomeric matrix, whilefacilitating the dispersion of this inorganic filler within said matrix.

“Coupling agent” is more precisely understood to mean an agent capableof establishing a sufficient chemical and/or physical connection betweenthe particular filler and the elastomer, while facilitating thedispersion of the filler within the elastomeric matrix. Such a couplingagent, which is at least bifunctional, may have, for example, thesimplified general formula “Y—T—X”, wherein: (1) Y represents afunctional group (“Y function”) which is capable of bonding physicallyand/or chemically with the inorganic filler, where such a bond may beestablished, for example, between a silicon atom of the coupling agentand the hydroxyl (OH) surface groups of the inorganic filler (forexample, the surface silanols in the case of silica); (2) X represents afunctional group (“X function”) which is capable of bonding physicallyand/or chemically with the elastomer, for example, by means of a sulfuratom; and (3) T represents a group linking Y and X.

The coupling agents must not be confused with simple agents for coveringthe particular filler, where such simple covering agents, in knownmanner, may comprise the Y function, which is active with respect to thefiller, but are devoid of the X function which is active with respect tothe elastomer.

Such coupling agents, of variable effectiveness, have been described ina large number of documents and are well-known to the person skilled inthe art. In fact, any known coupling agent known to or likely to ensure,in the diene rubber compositions which can be used for the manufactureof tires, the effective bonding or coupling between a reinforcinginorganic filler, such as silica, and a diene elastomer may be used. Forexample, organosilanes, particularly polysulfurized alkoxysilanes ormercaptosilanes, or polyorganosiloxanes bearing the X and Y functionsmentioned above may be used.

Silica/elastomer coupling agents in particular have been described in alarge number of documents, where the best known of such coupling agentsare bifunctional alkoxysilanes such as polysulfurized alkoxysilanes. Inparticular, polysulfurized alkoxysilanes, which are referred to as“symmetrical” or “asymmetrical” depending on their specific structure,may be used, such as those described, for example, in U.S. Pat. Nos.3,842,111; 3,873,489; 3,978,103; 3,997,581; 4,002,594; 4,072,701; and4,129,585, or in the more recent U.S. Pat. Nos. 5,580,919; 5,583,245;5,650,457; 5,663,358; 5,663,395; 5,663,396; 5,674,932; 5,675,014;5,684,171; 5,684,172; 5,696,197; 5,708,053; and 5,892,085; and EuropeanPatent No. EP 1 043 357, all of which describe such known compounds indetail.

Particularly suitable for implementing the present invention (withoutthe definition below being limiting) are symmetrical polysulfurizedalkoxysilanes, which satisfy the following general formula (I):

 Z—A—S_(n)—A—Z  (I)

wherein: n is an integer from 2 to 8 (preferably from 2 to 5); A is adivalent hydrocarbon radical (preferably C₁-C₁₈ alkylene groups orC₆-C₁₂ arylene groups, more particularly C₁-C₁₀ alkylenes, moreparticularly C₁-C₄ alkylenes, more particularly propylene); and Zcorresponds to one of the formulae below:

wherein: the radicals R¹, which may or may not be substituted, and maybe identical or different, represent a C₁-C₁₈ alkyl group, a C₅-C₁₈cycloalkyl group, or a C₆-Cl₁₈ aryl group, (preferably C₁-C₆ alkylgroups, cyclohexyl or phenyl, in particular C₁-C₄ alkyl groups, moreparticularly methyl and/or ethyl); and the radicals R², which may or maynot be substituted, and may be identical or different, represent aC₁-C₁₈ alkoxyl group or a C₅-C₁₈ cycloalkoxyl group (preferably C₁-C₈alkoxyl groups or C₅-C₈ cycloalkoxyl groups, more preferably C₁-C₄alkoxyl groups, in particular methoxyl and/or ethoxyl).

In the case of a mixture of polysulfurized alkoxysilanes in accordancewith Formula (I) above, particularly conventional, commerciallyavailable mixtures, it will be understood that the average value of “n”is a fractional number, preferably within the range of from 2 to 5.

Polysulfurized alkoxysilanes appropriate for use herein include: thepolysulfides (in particular, disulfides, trisulfides or tetrasulfides)of bis-(alkoxyl(C₁-C₄)-alkyl(C₁-C₄)silylalkyl(C₁-C₄)), such as, forexample, the polysulfides of bis(3-trimethoxysilylpropyl) or ofbis(3-triethoxysilylpropyl). Of these compounds, preferablybis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT, of theformula [(C₂H₅O)₃Si(CH₂)₃S]₂, or bis(triethoxysilylpropyl) disulfide,abbreviated TESPD, of the formula [(C₂H₅O)₃Si(CH₂)₃S]₂, are used. TESPDis commercially available, for example, from Degussa under the namesSi266 or Si75 (in the latter case, in the form of a mixture of disulfide(75% by weight) and of polysulfides), or alternatively from Witco underthe name Silquest A1589. TESPT is commercially available, for example,from Degussa under the name Si69 (or X50S when it is supported to 50% byweight on carbon black), or alternatively from Osi Specialties under thename Silquest A1289 (in both cases, a commercial mixture of polysulfideshaving an average value of n which is close to 4).

The compositions according to the invention also comprise, in additionto the diene elastomers having carboxylic acid functions along the chainand said reinforcing inorganic filler, plasticizers, pigments,antioxidants, anti-ozone waxes, a cross-linking system based on sulfurand/or on peroxide and/or on bismaleimides, cross-linking activatorscomprising zinc monoxide and stearic acid, extender oils, one or moreagents for covering the silica, such as alkoxysilanes, polyols oramines.

In particular, these compositions may be such that the diene elastomerhaving carboxylic acid functions is extended using a paraffinic,aromatic or naphthenic oil, with a quantity of extender oil of between 0and 50 phr.

Another subject of the present invention is a process for thepreparation of a cross-linkable rubber composition according to theinvention. In known manner, such a process comprises: (1) a first phaseof thermomechanical working of the constituents of the composition (withthe exception of the cross-linking system) carried out at a maximumtemperature of between 130° C. and 200° C., which is followed by (2) asecond phase of mechanical working effected at a temperature less thanthat of the first phase and during which the cross-linking system isincorporated.

The first phase comprises the stages of: (1) mixing together theconstituents of the first phase, with the exception of the antioxidant;and (2) incorporating the antioxidant and mixing it with theconstituents of the first stage of the first phase. Furthermore, zincmonoxide is conventionally added during the second stage to activate thelater cross-linking.

It has been discovered unexpectedly that incorporating all the zincmonoxide during the first stage of thermomechanical working, contrary toconventional methods in which the zinc monoxide is incorporated duringthe second stage of thermomechanical working, makes it possible tominimize further the hysteresis losses at low deformations of thecomposition according to the invention in the cross-linked state whichcorresponds to the above definition. At the same time that thehysteresis losses are being minimized, this incorporation of the zincmonoxide during the first stage of thermomechanical working also impartsto the composition according to the present invention processingproperties, in the non-cross-linked state, which are still improvedcompared with the processing properties of compositions based on knownfunctional elastomers and processing properties which are comparable tothe processing properties of compositions according to the inventionwhere the incorporation of zinc monoxide occurs during the second stageof thermomechanical working.

It has also been discovered unexpectedly that the incorporation ofmagnesium monoxide during the first stage of thermomechanical workingmakes it possible to minimize further the hysteresis losses at low andhigh deformations of the composition according to the invention in thecross-linked state corresponding to the aforementioned definition, whileimparting to the composition according to the invention processingproperties in the non-cross-linked state which are similar to theprocessing properties of compositions based on non-functionalelastomers.

Another subject of the present invention is a tread for a tire, wherethe tread comprises a cross-linkable or cross-linked rubber compositionaccording to the invention described in detail above or where the treadis formed of this composition. Because of the reduced hysteresis thatcharacterizes a rubber composition according to the present invention inthe cross-linked state, it will be noted that a tire, where the tread ofthe tire comprises the composition of the present invention, has theadvantage of reduced rolling resistance. Thus, another subject of thepresent invention includes a tire, such that the tire comprises thetread made up of the composition of the present invention.

The aforementioned characteristics of the present invention, as well asothers, will be better understood upon reading the following descriptionof several examples of embodiments of the invention, which are given byway of illustration and not of limitation.

EXAMPLES

For the polymers described herein, the viscosities indicated areinherent viscosities which are measured at a concentration of 1 g/L intoluene at 25° C.

The following experimental techniques were used in characterizing thepolymers obtained:

a) The SEC technique (size exclusion chromatography technique) was usedto determine the distributions of molecular weights relative to samplesof these polymers. Starting from standard products whose characteristicsare described in Example 1 of European Patent No. EP 0 692 493, thistechnique made it possible to evaluate, for a sample, a number-averagemolecular weight (M_(n)) which has a relative value, unlike the onedetermined by osmometry, and also a weight-average molecular weight(M_(w)). The polydispersity index (I_(p=M) _(w)/M_(n)) of the sample wasdeduced therefrom.

According to this technique, the macromolecules are separated physicallyaccording to their respective sizes when swollen, in columns filled witha porous stationary phase. Before implementing this separation, thesample of polymer is solubilized at a concentration of about 1 g/L intetrahydrofuran.

A chromatograph sold under the name/model “WATERS 150C” was used for theaforementioned separation. The elution solvent was tetrahydrofuran, theflow rate was 1 mL/min, the temperature of the system was 35° C. and theduration of analysis was 30 minutes. A set of two “WATERS” columns isused, the type being “STYRAGEL HT6E”.

The injected volume of the solution of the polymer sample was 100 μL.The detector used was a “WATERS R401” differential refractometer.Software for processing the chromatographic data was also used, thetrade name of which is “WATERS MILLENNIUM”.

b) Additionally, with the aim of calculating the amount of COOHfunctions (in meq/kg of polymer) and the number of correspondingfunctional units per chain of polymer, a metering method using the ¹HNMR technique was used, after esterification with an excess ofdiazomethane, which reagent is known to react with COOH functions.

More precisely, this method consists of using diazomethane, methyl esterfunctions from the COOH functions which have been fixed to theelastomer, in order to provide access indirectly and quantitatively tothe amounts of COOH functions by ¹H NMR. The diazomethane is prepared asfollows: It is obtained by action of alcoholic potassium hydroxidesolution on N-methyl-N-nitrosoparatoluenesulfonamide, in the presence ofdiethyl ether at the temperature of melting ice. Then the ether phasecontaining the reagent is recovered by simple distillation.

The esterification reaction is then carried out in the following manner:A sample of the elastomer which has been washed and dried in a specificmanner is solubilized in toluene, so as to be able to characterize it byanalysis. This specific preparation consists of treating the elastomerby three successive dissolution operations in toluene, respectively,followed by coagulation operations in a mixture formed of acetone andwater and which is acidified to pH=2 with hydrochloric acid, in order toeliminate any traces of acidic compounds (stopper, antioxidant,catalytic residues, by-products such as isovaleric acid, in particular).Then the elastomer thus treated is dried in an oven at 50° C., in avacuum and under a nitrogen atmosphere.

Then, the ethereal solution containing the diazomethane is addedthereto, such that there is an excess of reagent relative to the COOHfunctions. The polymer thus treated is subsequently coagulated inmethanol, then redissolved twice in toluene and methanol to coagulateit. The polymer is then dried in a desiccator at ambient temperature andunder a high vacuum by means of a vane pump.

¹H NMR analysis is then performed in the following manner: A sample ofthe polymer, esterified in the manner described above, is solubilized incarbon disulfide. The ¹H NMR signal is analyzed using a spectrometercommercially available under the name BRUKER AC200. The characteristicsignal of the three methyl protons of COOCH₃ provides quantitativeaccess to the initial proportion of COOH functions in the functionalpolymer.

In the following examples, the properties of the compositions accordingto the present invention were evaluated as follows:

The Mooney viscosity ML (1+4) at 100° C., was measured in accordancewith ASTM Standard D-1646 and is referred to as Mooney in the tables.

The Moduli of elongation at 300% (ME 300), at 100% (ME 100) and at 10%(ME 10) were measured. These measurements were taken in accordance withStandard ISO 37.

The Scott break indices were measured at 20° C., while the Breaking load(BL) was measured in MPa. The elongation at break (EB) was measured in%.

The hysteresis losses (HL) were measured by rebound at 60° C. in %. Thedeformation for the losses measured is about 40%. The Shore A hardnessmeasurements were taken in accordance with Standard DIN 53505.

The dynamic shear properties measurements are taken as a function of thedeformation and are performed at 10 Hertz with a peak-to-peakdeformation of from 0.15% to 50%. The non-linearity expressed is thedifference in the shear modulus between 0.15% and 50% deformation, inMPa. The hysteresis is expressed by the measurement of tan δ max. at 23°C. in accordance with Standard ASTM D2231-71 (reapproved in 1977).

Example 1 Preparation of Styrene/butadiene Copolymers (SBR), WhetherFunctionalized or Not

(A) Preparation Discontinuously and in Solution of a Non-functional SBR(“S-SBR A”):

In the first phase, a styrene/butadiene copolymer was prepared byinjecting 167 grams of styrene, 476 grams of butadiene and 2000 ppm oftetrahydrofuran (THF) into a 10 liter reactor containing 6.4 liters ofdeaerated heptane. The impurities are neutralized using n-BuLi. Then0.0038 mol of n-BuLi and 0.0011 mol of sodium tert. butylate used asrandomizing agent were added. The polymerization was carried out at 55°C.

In the second phase, at 90% conversion, 0.006 mol of methanol wasinjected into the reactor. The polymer solution was stirred for 15minutes at 55° C. The polymer was antioxidized by the addition of 0.8phr of 2,2′-methylene bis(4-methyl-6-tert. butylphenol) and 0.2 phr ofN-(1,3-dimethylbutyl)-N′-p-phenylenediamine. The polymer was thenrecovered by steam stripping and dried on an open mill at 100° C.

The S-SBR A thus obtained had the following characteristics:

Incorporated styrene 26% by weight Number of vinyl units of thebutadiene fraction 41% Viscosity measured in toluene at 25° C. (dL/g) 1.4 Mooney viscosity ML (1 + 4, 100° C.) 26 M_(n) measured by osmometry155,000 g/mol. polydispersity index  1.07.

(B) Preparation Discontinuously and in Solution of a Functionalized SBRby Reaction with Hexamethylcyclotrisiloxane (“S-SBR B”):

In the first phase, operation was under conditions identical to thosedescribed in Example 1(A) above for the preparation of the S-SBR A.

In the second phase, at 90% conversion, an aliquot part was taken fromthe reactor, and the reaction was stopped by adding methanol. Theviscosity of the polymer was then measured to be 1.4 dL/g. Then, 0.0013mol of hexamethylcyclotrisiloxane (D3) was injected into the remainingcontents of the reactor. The polymer solution was stirred for 15 minutesat 55° C. The polymer was antioxidized by the addition of 0.8 phr of2,2′-methylene bis(4-methyl-6-tert. butylphenol) and 0.2 phr ofN-(1,3-dimethylbutyl)-N′-p-phenylenediamine. The polymer was thenrecovered by steam stripping and was dried on an open mill at 100° C.

The S-SBR B thus obtained had the following characteristics:

Incorporated styrene 26% by weight Number of vinyl units of thebutadiene fraction 41% Viscosity measured in toluene at 25° C. (dL/g) 1.4 Mooney viscosity ML (1 + 4, 100° C.) 26 M_(n) measured by osmometry155,000 g/mol. Polydispersity index  1.07.

The amount of functionalized chains was measured by ¹H NMR, afterpurification of the polymer sample by a series of three coagulationoperations in methanol, redissolving in toluene. This amount offunctionalized chains is expressed by means of this technique inmilli-equivalents per kilogram of polymer (meq/kg). The ¹H NMR spectrumwas characterized by blocks at 0 and −0.1 ppm corresponding to the—Si(CH₃)₂-OH group. For the S-SBR B, ¹H NMR analysis provided an amountof functions of 4.5 meq/kg which, taking into account the molecularweight M_(n) of the polymer, corresponds to approximately 70% offunctionalized chains.

(C) Preparation Discontinuously and in Solution of Several SBR'sComprising Carboxylic Acid Functions Along the Chain (“S-SBR C”, S-SBRD” and “S-SBR E”):

In this example, the number-average molecular weights (M_(n)) of thestarting polymers and the corresponding functional polymers weredetermined precisely by osmometry. The aforementioned SEC technique wasalso used to determine the distributions of molecular weights relativeto samples of these polymers.

Each of the three functional copolymers S-SBR C, S-SBR D and S-SBR E wasprepared using the same deoxygenated solution of a startingstyrene/butadiene copolymer, the number-average molecular weight ofwhich, determined by osmometry, was M_(n)=180,000 g/mole and thepolydispersity index of which, determined by the SEC technique, wasI_(p)=1.09.

The percentages of styrene, of 1,4-cis linkages, of 1,4-trans linkagesand of 1,2 linkages of this starting copolymer were 25%, 28%, 32% and40%, respectively.

Furthermore, this starting solution contained 0.2 phr of the antioxidantN-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine and 0.2 hr of theantioxidant 2,2′-methylene-bis (4-methyl-6-t. butylphenol).

In accordance with techniques known to the person skilled in the art andunder the conditions mentioned in Table 1 below, there was introduced,at ambient temperature into a 10 liter reactor containing 7 liters ofsaid deoxygenated solution, the necessary quantity of a molar toluenesolution of diisobutylaluminum hydride (HDiBA), the weight fraction ofthe polymeric solution in the toluene being 10%.

The reaction medium was stirred for 10 minutes in order to homogenize itsufficiently. Then, the stirring was stopped and the hydroaluminationwas effected under static conditions at 65° C. for 64 hours.

It will be noted that the value of the ratio of the number of moles ofHDiBA to kg of polymer was varied in order to prepare the threefunctional elastomers S-SBR C, S-SBR D and S-SBR E. Thus, this ratio was0.05 mol/kg, 0.1 mol/kg and 0.2 mol/kg for S-SBR C, S-SBR D and S-SBR E,respectively.

Then the functionalization was effected in the same reactor at 65° C.and for 6 hours, by means of pressurization of 6 bars with carbondioxide. This functionalization was performed under identical operatingconditions for the preparation of the elastomers S-SBR C, S-SBR D andS-SBR E.

Then, the reaction was stopped, first with acetylacetone in a molarratio of acetylacetone/aluminum of 12, and then with hydrochloric acidin a molar ratio of hydrochloric acid/aluminum of 7.5. Subsequently, theelastomer solution obtained was treated with 0.3 phr of an antioxidantconsisting of 2,2′-methylene-bis (4-methyl-6-t. butylphenol). Thenstripping, preferably with steam, was effected in acidic medium (pH=2).Then, the elastomer was re-dissolved in toluene, with concentratedaqueous hydrochloric acid, such that the molar ratio of hydrochloricacid/aluminum is equal to 5.

Then, a second stripping in acidic medium was effected in order to beable to eliminate the residual isovaleric acid completely. Isovalericacid is a by-product of the carboxylation of the isobutyl radicalscontained in the HDiBA.

The elastomer thus treated was then drained on a open mill at 100° C.,and was dried in a vacuum at 60° C. (with an inert nitrogen atmosphere)for 18 hours.

The amount of carboxylic acid functions was calculated (in meq/kg ofpolymer), and the number of corresponding functional units per chain ofcopolymer was calculated (with M_(n)=180,000 g/mole, determined byosmometry) using two different methods for each of these twocalculations.

The first method consisted of metering the carboxylic acid functions byacidimetry and calculating, on one hand, the amount of these COOHfunctions per kg of polymer and, on the other hand, the number of unitsper chain on the basis of a M_(n) (determined by osmometry) of 180,000g/mole.

This metering by acidimetry was effected by dissolving a sample of theelastomer thus prepared in a mixture of toluene andorthodichlorobenzene. The COOH functions are neutralized in the presenceof pyridine, with a solution of tetrabutylammonium hydroxide inisopropanol. The equivalence is detected by potentiometry.

The second method consisted of effecting metering in accordance with the¹H NMR technique described above in Section “b)” (beginning withparagraph 87 herein).

The results obtained are set forth in Table 1 below, which refers to thestarting styrene-butadiene copolymer and to the three copolymers S-SBRC, S-SBR D and S-SBR E which were hydroaluminized and functionalized.The amounts of COOH functions and the numbers of COOH units per chainwere determined in accordance with one or the other of the above twomethods indicated in Table 1 below.

TABLE 1 Amount of COOH Mooney functions (meq/kg) Hydroaluminationviscosity Inherent M_(n) No. COOH units/chain (No. moles of ML viscosity(SEC) I_(p) T_(g) Esterification HDiBA/kg SBR) (1 + 4) (dL/g) g/mole(SEC) (° C.) Acidimetry and ¹H NMR Starting 30 1.43 138000 1.09 −40S-SBR S-SBR C 0.05 32 1.51 132000 1.11 −40  4 meq/kg  5 meq/kg 1 unit 1unit S-SBR D 0.1 34 1.48 139000 1.11 −39 22 meq/kg 21 meq/kg 4 units 4units S-SBR E 0.2 38 1.42 140000 1.11 −38 44 meq/kg 40 meq/kg 8 units 7units

It will be noted that the functional polymers S-SBR C, S-SBR D and S-SBRE obtained have a macrostructure which is practically identical to thatof the starting polymer, as shown by the results of the distribution ofthe molecular weights (the polydispersity indices, I_(p)).

(D) Preparation in Emulsion of a Non-Functional SBR (“E-SBR F”):

The polymerization operations in this example were effected at 5° C.with stirring, in 250 mL Steinie bottles, in accordance with methodsknown to the person skilled in the art. The water used was deionized andbubbled through in a current of nitrogen to eliminate any trace ofdissolved oxygen.

An emulsifying solution consisting of 5.45 grams of n-dodecylamine, 1.59grams of acetic acid and 543.5 mL of water was introduced into a 750 mLSteinie bottle, which had previously been bubbled through with nitrogen.This emulsifying solution was heated to 60° C. and was stirred until then-dodecylamine has completely dissolved.

Then, 6.5 mL of a solution of 100 g/L KCl, 6.5 mL of a solution of 100g/L. AlCl₃ and 23 mL of a molar solution of hydrochloric acid were addedto this bottle.

45 mL of this stock solution was placed in a 250 mL Steinie bottle andcooled to 5° C. Then, 13 grams of liquid butadiene and 12 grams ofstyrene were added thereto. The whole was stirred in a tank at 5° C.until a stable emulsion formed. Finally, 2 mL of a solution of 31.25 g/Ln-dodecylmercaptan and 14.25 g/L paramenthane hydroperoxide was added,and the polymerization was started at 5° C. with stirring. Thepolymerization was stopped after 6 hours and 30 minutes by adding 0.025grams of hydroquinone.

10 grams of NaCl per 100 grams of elastomer was added to this emulsion,and the mixture was stirred for several minutes. Then, 150 mL of tolueneand 1 phr of an antioxidant mixture comprising 80% of the product named“AO2246” and 20% N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine(commonly called “6PPD”) were added. The solution was stirred onceagain. It was finally stripped, and the polymer was dried at between 30and 50° C.

15 g of a polymer having the characteristics indicated below in Table 2were obtained.

TABLE 2 T_(g)/ΔT % Butadiene** ML (1 + 4) Viscosity M_(n) (SEC) I_(p) (°C.) (1,4) trans (1,4) cis % styrene* 45 1.8 129443 3.72 −33/8 73.1 13.341.2 *This percentage is a mass percentage **These percentages are masspercentages relative to the incorporated butadiene.

(E) Preparation in Emulsion of an SBR Comprising Carboxylic AcidFunctions Along the Chain (“E-SBR G”):

The procedure followed was as described in Example 1(D) above, exceptthat 55 meq/kg of monomers of acrylic acid was added to the emulsifyingsolution, at the same time as the KCl and the AICl₃.

The polymerization was stopped after 18 hours by adding 0.025 grams ofhydroquinone. The polymer was recovered in the same manner as describedin Example 1(D) above. 15 g of a polymer having the characteristicsindicated below in Table 3 were obtained.

TABLE 3 T_(g)/ΔT % Butadiene** —COOH ML (1 + 4) Viscosity M_(n) (SEC)I_(p) (° C.) (1,4) trans (1,4) cis % styrene* (meq/kg) 49 1.76 1103453.23 −32/7 75 12 39 30

Furthermore, the E-SBR G thus obtained has a total quantity ofemulsifier which is less than 3 phr, as the treatment of the polymerobtained by solubilization and stripping has the effect of reducing thefinal quantity of emulsifier in the E-SBR G.

(F) Preparation in Emulsion of a Non-Functional SBR Extended with Oil(“E-SBR H”):

The polymerization operations were effected at 5° C. with stirring, in a10 liter stainless steel reactor, in accordance with the methods knownto the person skilled in the art. The water used was deionized andbubbled through in a current of nitrogen to eliminate any trace ofdissolved oxygen.

An emulsifying solution consisting of 37.19 grams of n-dodecylamine,10.95 grams of acetic acid and 540 mL of water was introduced into a 750mL Steinie bottle, bubbled through with nitrogen. This emulsifyingsolution was heated to 60° C. and stirred until the n-dodecylamine hadcompletely dissolved.

3 liters of water was added to the 10 liter reactor and was bubbledthrough under nitrogen for 30 minutes. All the soap solution wasintroduced into the reactor, as was 90 mL of a solution of 50 g/L KCl,90 mL of a solution of 100 g/L AlCl₃, 114 mL of a solution of 14 g/LFeCl₂ and 177 mL of a molar solution of hydrochloric acid.

The reactor was cooled to 12° C. and 1164 grams of butadiene and 1006grams of styrene were added thereto. The temperature of the reactor waslowered to 5° C. After 5 minutes' stirring, 2.55 grams of paramenthanehydroxide and 10.52 grams of mercaptan both diluted in 68 grams ofstyrene were added.

After 9 hours, the polymerization was stopped by adding 128 mL of asolution of 40 g/L hydroquinone. There was added thereto, successively,with stirring, 7 liters of toluene, 15 phr NaCl (15 g per 100 g ofelastomer), another 7 liters of toluene and 1 phr of a mixture ofantioxidants composed of 80% of the product “AO 2246” and 20% “6PPD”.The solution obtained was stripped and dried. The final conversion was74%.

The polymer was then solubilized in toluene and extended with 27.5 phrof an aromatic oil sold by BRITISH PETROLEUM under the name “EXAROL.”The polymer was finally dried in an oven in a vacuum at a temperature ofbetween 40 and 50° C.

The characteristics of the polymer obtained are indicated in Table 4below.

TABLE 4 T_(g)/ΔT % Butadiene** ML (1 + 4) Viscosity M_(n) (SEC) I_(p) (°C.) (1,4) trans (1,4) cis (1,2) % styrene* 50 2.35 124000 2.78 −30 75.511.6 12.9 41.1

(G) Preparation in Emulsion of an SBR Comprising Carboxylic AcidFunctions Along the Chain and Extended with Oil (“E-SBR I”):

The procedure for the polymerization was as described in Example 1(F)above, except that 5.78 grams of methacrylic acid was added to theemulsifying solution.

The polymerization was stopped after nine hours and thirty minutes, andthe conversion was 70%. Contrary to Example 1(F) above, 27.5 phr of thearomatic oil “EXAROL” was added to the polymer obtained beforeproceeding with the stripping, and the pH of the stripping water waskept at pH=2.

The polymer was dried in an oven under nitrogen at 30° C. and was usedin this form for the rubber properties tests. (See Example 2 below.) Thecharacteristics of the dry polymer included a Mooney viscosity ML(1+4)of the polymer extended with oil of 48. Additional characteristics ofthe dry polymer are set forth in Table 5 below:

TABLE 5 T_(g)/ΔT % Butadiene** —COOH Viscosity M_(n) (SEC) I_(p) (° C.)(1,4) trans (1,4) cis (1,2) % styrene* (meq/kg) 2.23 108581 3.2 −31/975.4 11.8 12.8 41.0 31

Furthermore, the E-SBR I thus obtained had a total quantity ofemulsifier which was less than 3 phr, as the treatment of the polymerobtained by solubilization and stripping has the effect of reducing thefinal quantity of emulsifier in the E-SBR I.

Example 2 Rubber Compositions Comprising an Inorganic Reinforcing Fillerand the Aforementioned Elastomers

(A) First Comparative Example:

In this example, five of the clastomers of Example 1 above(specifically, S-SBR A, S-SBR B, S-SBR C, S-SBR D and S-SBR E) were usedfor the preparation of rubber compositions A, B, C, D and E of thepassenger-car-tread type.

Each of these compositions A, B, C, D and E had the followingformulation (expressed in phr: parts by weight per hundred parts ofelastomer):

Elastomer 100 Silica (1) 80 Aromatic oil (“ENERFLEX 65”) 40 Bondingagent (2) 6.4 ZnO 2.5 Stearic acid 1.5 Antioxidant (3) 1.9 Anti-ozonewax “C32ST” 1.5 Sulfur 1.1 Sulfenamide (4) 2 Diphenylguanidine 1.5wherein: (1) = The silica “Zeosil 1165MP” manufactured by Rhodia; (2) =The bonding agent “Si69” from Dégussa; (3) =N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine; and (4) =N-cyclohexyl-2-benzothiazylsulfenamide.

Each of the following compositions was produced, in a first phase ofthermomechanical working, by two stages separated by a cooling phase,then, in a second, finishing, phase, by mechanical working.

There were introduced in succession into a laboratory internal mixer ofthe “Banbury” type, the capacity of which is 400 cm³, which is 70%filled and the initial temperature of which is approximately 90° C., theelastomer, two-thirds of the reinforcing filler, the coupling agent, thediphenylguanidine and the stearic acid. Then, approximately one minutelater, the rest of the reinforcing filler, the aromatic oil and theanti-ozone wax “C32ST” were introduced.

The first thermomechanical working stage was performed for 4 to 5minutes, until a maximum dropping temperature of about 160° C. wasachieved. The elastomeric block was then recovered and cooled.

Then, a second stage of thermomechanical working was performed in thesame mixer for 3 to 4 minutes, with addition of the antioxidant and thezinc monoxide, until a maximum dropping temperature of about 160° C. wasachieved.

The aforementioned first phase of thermomechanical working was thuseffected, it being specified that the average speed of the blades duringthis first phase was 45 rpm.

The mixture thus obtained was recovered and cooled. Then, in an externalmixer (homo-finisher), the sulfur and sulfenamide were added at 30° C.,by mixing everything for 3 to 4 minutes (This constituted theaforementioned second phase of mechanical working).

The compositions thus obtained were then calendered either in the formof sheets (of a thickness of 2 to 3 mm) or of fine films of rubber inorder to measure their physical or mechanical properties, or in the formof profiled elements which can be used directly, after cutting outand/or assembly to the dimensions desired, for example, as semi-finishedproducts for tires, in particular for treads.

The cross-linking was carried out at 150° C. for 40 minutes. The resultsare set forth in Table 6 below.

TABLE 6 C D E A B S-SBR C S-SBR D S-SBR E COMPOSITION S-SBR A S-SBR B 1unit 4 units 8 units ML (1 + 4) rubber at 100° C. 26 26 32 34 38Properties in the non-cross-linked state ML (1 + 4) at 100° C. 53 85 5664 71 (“Mooney mixture”) Properties in the cross-linked state Shore 65.658.4 63.7 61.2 62.6 ME10 5.52 3.66 4.77 4.23 4.33 ME100 1.74 1.62 1.751.83 2.07 ME300 1.99 2.34 2.11 2.43 2.78 ME300/ME100 1.14 1.44 1.20 1.331.34 Scott break index at 20° C. BL 20.0 23.4 20.1 20.6 21.0 EB % 571533 537 491 483 Losses 60° C. (def. 40%) 33.0 21.3 31.3 27.3 25.7Dynamic properties as a function of deformation Delta G* at 23° C. 4.031.16 2.50 1.14 0.61 Tan δ max at 23° C. 0.352 0.229 0.297 0.213 0.163

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 relating tocompositions B, C, D and E (based on S-SBR B, S-SBR C, S-SBR D and S-SBRE, respectively) is greater than that relating to composition A and, onthe other hand, that the hysteresis properties (at low and highdeformations) are greatly improved compared with those of composition A.

It will also be noted that the compositions C, D and E according to theinvention have values of Mooney “mixture” which are distinctly less thanthat of composition B based on an elastomer functionalized by reactionwith hexamethylcyclotrisiloxane. These Mooney values are indicative of aprocessing ability for the compositions of the invention which isimproved compared to that of a composition based on a known functionalelastomer.

These Mooney values for compositions C, D and E are close to that ofcomposition A based on a non-functional elastomer S-SBR A. Particularly,the Mooney values for composition C and D are close to that ofcomposition A, while the Mooney value for composition E according to theinvention is between those of compositions A and B.

In other words, the elastomers S-SBR C, S-SBR D and S-SBR E whichcomprise COOH functions along the chain and, more particularly, S-SBR D,impart to compositions filled with silica practically the same rubberproperties in the cross-linked state as those imparted to such acomposition by a known functional elastomer, and furthermore with aprocessing ability close to that imparted by a non-functional elastomer.

(B) Second Comparative Example:

In this example, the non-functional S-SBR A from Example 1 above wasused to prepare a rubber composition A′ of the passenger-car-tread type,which is distinguished from the aforementioned composition A in that itfurthermore comprises a carboxylic acid.

An attempt was made to compare the properties of the aforementionedcomposition D according to the present invention with the properties ofcomposition A′.

Each of the compositions A and D had the following formulation(expressed in phr: parts by weight per hundred parts of elastomer):

Elastomer 100 Silica (1) 80 Aromatic oil (“ENERFLEX 65”) 40 Bondingagent (2) 6.4 ZnO 2.5 Stearic acid 1.5 Antioxidant (3) 1.9 Anti-ozonewax “C32ST” 1.5 Sulfur 1.1 Sulfenamide (4) 2 Diphenylguanidine 1.5wherein: (1) = The silica “Zeosil 1165MP” manufactured by Rhodia; (2) =The bonding agent “Si69” from Dégussa; (3) =N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine; and (4) =N-cyclohexyl-2-benzothiazylsulfenamide.

More precisely, the carboxylic acid used for composition A′ was oleicacid, and it was incorporated in the S-SBR A prior to the addition ofthe other additives, so as to be able to effect a first jointmastication of the S-SBR A and the oleic acid. The amount of oleic acidwhich was added to the S-SBR A was 0.62 phr, which corresponds to astoichiometry of 4 units which are fixed to the elastomer chain, byanalogy with the S-SBR D of the invention. (Thus, the composition A′ hasthe formulation shown above for the compositions A and D, furthermorecomprising 0.62 phr of oleic acid.)

Each of the following compositions was produced, in a first phase ofthermomechanical working, by two stages separated by a cooling phase,then, in a second, finishing, phase, by mechanical working.

There were introduced in succession into a laboratory internal mixer ofthe “Banbury” type, the capacity of which is 400 cm³, which was 70%filled and the initial temperature of which was approximately 90° C.,the elastomer, two-thirds of the reinforcing filler, the coupling agent,the diphenylguanidine and the stearic acid. Then, approximately oneminute later, the rest of the reinforcing filler, the aromatic oil andthe anti-ozone wax “C32ST” were introduced.

The first thermomechanical working stage was performed for 4 to 5minutes, until a maximum dropping temperature of about 160° C. wasachieved. The clastomeric block was then recovered and cooled.

Then a second stage of thermomechanical working was performed in thesame mixer for 3 to 4 minutes, with addition of the antioxidant and thezinc monoxide, until a maximum dropping temperature of about 160° C. wasachieved.

The aforementioned first phase of thermomechanical working was thuseffected, it being specified that the average speed of the blades ofthis first phase was 45 rpm.

The mixture thus obtained was recovered and cooled. Then, in an externalmixer (homo-finisher), the sulfur and sulfenamide were added at 30° C.,by mixing everything for 3 to 4 minutes. (Thus, this constituted thesecond mechanical working phase.)

The compositions thus obtained were then calendered, either in the formof sheets (of a thickness of 2 to 3 mm) or of fine films of rubber inorder to measure their physical or mechanical properties, or in the formof profiled elements which can be used directly, after cutting outand/or assembly to the dimensions desired, for example, as semi-finishedproducts for tires, in particular for treads.

The cross-linking was carried out at 150° C. for 40 minutes. The resultsare set forth in Table 7 below.

TABLE 7 D A S-SBR D A′ COMPOSITION S-SBR A 4 units S-SBR A ML (1 + 4)rubber at 100° C. 26 34 26 Properties in the non-cross-linked state ML(1 + 4) at 100° C. 53 64 41 Properties in the cross-linked state Shore65.6 61.2 65.0 ME10 5.52 4.23 5.23 ME100 1.74 1.83 1.73 ME300 1.99 2.431.92 ME300/ME100 1.14 1.33 1.11 Scott break index at 20° C. BL 20.0 20.620.4 EB % 571 491 597 Losses 60° C. (def. 40%) 33.0 27.3 30.2 Dynamicproperties as a function of deformation Delta G* at 23° C. 4.03 1.143.72 Tan δ max at 23° C. 0.352 0.213 0.316

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 relating tocomposition A′ is very close to that of composition A and, on the otherhand, that the hysteresis properties of composition A′ are notsubstantially improved compared with those of composition A.

In the light of these results, it will be noted that the elastomer S-SBRD which comprises COOH functions along the chain imparts to acomposition filled with silica a combination of characteristics(including processing ability/properties at low deformations) which isimproved overall when compared to the same combination ofcharacteristics relative to composition A′ comprising a carboxylic acid.

(C) Third Comparative Example:

In this example, the S-SBR B (functionalized by the reaction withhexamethylcyclotrisiloxane) and the S-SBR D of Example 1 above(comprising 4 COOH units along the chain) were used for the preparationof two rubber compositions B′ and D′, respectively, of thepassenger-car-tread type. These compositions B′ and D′ are distinct fromthe compositions B and D mentioned above in Example 2(A) only by theirrespective preparation processes. (Thus, each of these compositions B′and D′ has the same ingredients and the same formulation as in thepreceding Examples 2(A) and 2(B).)

Each of compositions B′ and D′ was produced, in a first phase ofthermomechanical working, by two stages separated by a cooling phase,then, in a second, finishing, phase, by mechanical working.

There were introduced in succession into a laboratory internal mixer ofthe “Banbury” type, the capacity of which is 400 cm³, which was 70%filled and the initial temperature of which was approximately 90° C.,the elastomer, two-thirds of the reinforcing filler, the coupling agent,the diphenylguanidine and the stearic acid. Then, approximately oneminute later, the rest of the reinforcing filler, the aromatic oil andthe anti-ozone wax “C32ST” were introduced.

The first thermomechanical working stage was performed for 4 to 5minutes, until a maximum dropping temperature of about 160° C. wasachieved. The elastomeric block was then recovered and cooled.

Then, a second stage of thermomechanical working was performed in thesame mixer for 3 to 4 minutes, with addition of the antioxidant and thezinc monoxide, until a maximum dropping temperature of about 160° C. wasachieved.

The aforementioned first phase of thermomechanical working was thuseffected, it being specified that the average speed of the blades ofthis first phase was 85 rpm (unlike in the examples of Example 2(A)above).

The mixture thus obtained was recovered and cooled. Then, in an externalmixer (homo-finisher), the sulfur and sulfenamide were added at 30° C.,by mixing everything for 3 to 4 minutes. (Thus, this constituted thesecond mechanical working phase.)

The compositions thus obtained were then calendered either in the formof sheets (of a thickness of 2 to 3 mm) or of fine films of rubber inorder to measure their physical or mechanical properties, or in the formof profiled elements which can be used directly, after cutting outand/or assembly to the dimensions desired, for example, as semi-finishedproducts for tires, in particular for treads.

The cross-linking was carried out at 150° C. for 40 minutes.

It will be noted that all the zinc monoxide (ZnO) was introducedconventionally in the second stage of thermomechanical working, in orderto obtain cross-linkable compositions B′ and D′.

In this comparative example, said S-SBR D was also used for thepreparation of a composition D″ of the passenger-car-tread type, wherethis composition D″ was distinct from the above-mentioned composition D′solely in that the introduction of all the zinc monoxide takes placeduring the first stage of thermomechanical working, and not, inconventional manner, during the second stage of thermomechanicalworking. (Thus, this composition D″ also has the same ingredients andthe same formulation as in 2(A) and 2(B) above.)

An attempt was made to compare the properties of compositions D′ and D″according to the invention with each other, on one hand, and with thoseof composition B′, on the other hand. The results are set forth in Table8 below:

TABLE 8 B′ D′ D″ COMPOSITION S-SBR B S-SBR D S-SBR D ML (1 + 4) rubberat 100° C. 26 34 34 Properties in the non-vulcanized state ML (1 + 4) at100° C. 92 51 49 (“Mooney mixture”) Properties in the vulcanized stateShore 58.1 61.3 61.2 ME10 3.52 3.94 3.96 ME100 1.69 1.58 1.59 ME300 2.312.03 2.08 ME300/ME100 1.37 1.29 1.31 Scott break index at 20° C. BL 23.420.1 22.0 EB % 533 537 604 Losses 60° C. (def. 40%) 16.7 28.0 27.3Dynamic properties as a function of deformation Delta G* at 23° C. 0.780.84 0.58 Tan δ max at 23° C. 0.186 0.193 0.172

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 relating to thepreferred composition D″ according to the invention is greater than thatof the other composition D′ according to the invention and, on the otherhand, that the hysteresis properties at low deformations of compositionD″ are improved compared with those of composition D′ and also comparedwith those of composition B′ (which is based on a functionalizedelastomer by reaction with hexamethylcyclotrisiloxane).

It will also be noted that composition D″ according to the invention hasa value of Mooney “mix” which is distinctly less than that ofcomposition B′. This Mooney value indicates a processing ability for thecomposition D″ according to the invention which is always improvedcompared to that of a composition based on a known functional elastomer.

In other words, the elastomer S-SBR D, which comprises COOH functionsalong the chain, imparts to composition D″, which is filled with silicaand is obtained by introducing ZnO during the first stage ofthermomechanical working, hysteresis properties at low deformationswhich are improved compared with those hysteresis properties imparted tosuch a composition by a known functional elastomer, and furthermore hasa processing ability which is identical, or even improved, when comparedwith the processing ability of composition D′, which is also based onelastomer S-SBR D, being filled with silica but is obtained byconventional introduction of ZnO during the second stage ofthermomechanical working.

(D) Fourth Comparative Example:

In this example, the properties of a new composition D′″ of the“passenger-car”-tread type based on said S-SBR D were compared withthose of compositions A, B′ and D′ tested in the preceding examples.(See Example 2(C) above for B′ and D′, where the introduction of the ZnOis during the second stage of thermomechanical working.)

Composition D′″ was produced in accordance with the method described inExample 2(C) above for composition D′; however, composition D′″ wasfurther characterized in that magnesium oxide (MgO) was added in aquantity of 1.33 phr in one go, right at the beginning of the firststage of thermomechanical working (namely at t=0 minutes in the internalmixer).

The results obtained are set forth in Table 9 below.

TABLE 9 A B′ D′ D′′′ COMPOSITION S-SBR A S-SBR B S-SBR D S-SBR D ML (1 +4) 100° C. 26 26 34 34 rubber Properties in the non-vulcanized state ML(1 + 4) at 100° C. 53 85 51 58 Properties in the vulcanized state ShoreA 65.6 58.1 61.3 59.9 ME10 (MPa) 5.52 3.52 3.94 3.60 ME100 (MPa) 1.741.69 1.58 1.80 ME300 (MPa) 1.99 2.31 2.03 2.49 ME300/ME100 1.14 1.371.29 1.38 Scott break index at 20° C. BL (MPa) 20.0 23.4 20.1 21.1 EB(%) 571 533 537 549 Losses 60° C. (def. 40%) 33.0 16.7 28.0 20.3 Dynamicproperties as a function of deformation ΔG* 23° C. (MPa) 4.03 0.78 0.840.26 Tan (δ)_(max) 23° C. 0.352 0.186 0.193 0.140

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 relating tocomposition D′″ according to the invention (based on S-SBR D withaddition of the MgO during the first stage of thermomechanical working)is substantially identical to that of composition B′ and, on the otherhand, that the hysteresis properties (losses at 60° C. and tan δ max at23° C.) are greatly improved when compared with the hysteresisproperties of composition A. These results also show that compositionD′″ makes it possible to obtain hysteresis properties at low and highdeformations which are improved compared with those of composition D′but also relative to composition B′ for the low deformations.

On the other hand, it would appear that composition D′″ has, in thenon-cross-linked state, a value of Mooney viscosity of mix which isdistinctly less than that of composition B′ and substantially close tothat of composition A based on a non-functional S-SBR. This compositionD′″ consequently has a processing ability which is distinctly improvedcompared with that of the compositions based on conventional functionalelastomers.

In other words, composition D′″ according to the invention hashysteresis properties at low deformations which are improved comparedwith those of a composition based on a conventional functional elastomerwhile considerably improving the hysteresis properties at highdeformations (losses at 60° C.) compared with those of composition D′without MgO. This composition D′″ furthermore has a processing abilitywhich is close to that of the “control” composition A based on anon-functional elastomer.

(E) Fifth Comparative Example:

In this example, the properties of a new composition D″″ of the“passenger-car”-tread type based on said S-SBR D were compared withthose of compositions A, B′, D′ and D′″ tested in the precedingexamples.

Composition D″″ was produced in accordance with the method described inExample 2(D) above for composition D′″; however, this composition D′″differed from said composition D′″ solely by the fact that theaforementioned 1.33 phr of magnesium oxide (MgO) was added in a singlego to the internal mixer during the first stage of thermomechanicalworking, only when the temperature in the internal mixer had reached120° C. (i.e., after about 2 to 3 minutes, contrary to composition D′″,in which this addition of MgO took place at t=0 minutes).

The results obtained are set forth in Table 10 below:

TABLE 10 A B′ D′ D′′′ D″″ COMPOSITION S-SBR A S-SBR B S-SBR D S-SBR DS-SBR D ML (1 + 4) 100° C. rubber 26 26 34 34 34 Properties in thenon-vulcanized state ML (1 + 4) 100° C. 53 92 51 58 58 Properties in thevulcanized state Shore A 65.6 58.1 61.3 59.9 57.9 ME10 (MPa) 5.52 3.523.94 3.60 3.50 ME100 (MPa) 1.74 1.69 1.58 1.80 1.74 ME300 (MPa) 1.992.31 2.03 2.49 2.42 ME300/ME100 1.14 1.37 1.29 1.38 1.39 Scott breakindex at 20° C. BL (MPa) 20.0 23.4 20.1 21.14 19.2 EB (%) 571 533 537549 505 Losses 60° C. (def. 40%) 33.0 16.7 28.0 20.3 20.1 Dynamicproperties as a function of deformation ΔG* 23° C. (MPa) 4.03 0.78 0.840.26 0.23 Tan (δ)_(max) 23° C. 0.352 0.186 0.193 0.140 0.138

It will be noted that composition D″″ according to the invention makesit possible to obtain properties in the non-cross-linked andcross-linked state which are similar to those of the other compositionD′″ according to the invention. Consequently, the moment of introductionof the MgO during the first stage of thermomechanical working does notchange the Mooney viscosity, the ratio ME300/ME100 and the hysteresisproperties obtained with said composition D′″.

In other words, composition D″″ makes it possible to obtain hysteresisproperties (tan δ max at 23° C.) which are largely improved comparedwith those of compositions A, B′ and D′, with a distinct improvement ofthe processing ability compared with that of composition B′ based on aknown functional elastomer. Furthermore, the compositions D′″ and D″″according to the invention have hysteresis properties at highdeformations which are improved compared with those of compositions A orD′.

(F) Sixth Comparative Example:

In this example, the properties of two rubber compositions F and G ofthe “passenger-car”-tread type were compared, composition F being basedon the non-functional E-SBR F of Example 1 (D) above and composition Gbeing based on E-SBR G comprising acrylic acid functions along the chain(see Example 1 (E) above).

The formulation used for each of these two compositions F and G was theone mentioned in Example 2(A) above.

Each of these two compositions F and G was produced, in a first phase ofthermomechanical working, by two stages separated by a cooling phase,then, in a second, finishing, phase, by mechanical working.

There were introduced in succession into a laboratory internal mixer ofthe “Banbury” type, the capacity of which is 400 cm³, which was 70%filled and the initial temperature of which was approximately 90° C.,the elastomer, two-thirds of the reinforcing filler, the coupling agent,the diphenylguanidine and the stearic acid. Then, approximately oneminute later, the rest of the reinforcing filler, the aromatic oil andthe anti-ozone wax “C32ST” were introduced.

The first thermomechanical working stage was performed for 4 to 5minutes, until a maximum dropping temperature of about 160° C. wasachieved. The elastomeric block was then recovered and cooled.

Then, a second stage of thermomechanical working was performed in thesame mixer for 3 to 4 minutes, with addition of the antioxidant and thezinc monoxide, until a maximum dropping temperature of about 160° C. wasachieved.

The aforementioned first phase of thermomechanical working was thuseffected, it being specified that the average speed of the blades ofthis first phase was 85 rpm.

The mixture thus obtained was recovered and cooled. Then, in an externalmixer (homo-finisher), the sulfur and sulfenamide were added at 30° C.,by mixing everything for 3 to 4 minutes. (Thus, this constituted thesecond mechanical working phase.)

The compositions thus obtained were then calendered, either in the formof sheets (of a thickness of 2 to 3 mm) or of fine films of rubber inorder to measure their physical or mechanical properties, or in the formof profiled elements which can be used directly, after cutting outand/or assembly to the dimensions desired, for example, as semi-finishedproducts for tires, in particular for treads.

The cross-linking was carried out at 150° C. for 40 minutes. It will benoted that all the zinc monoxide (ZnO) is in this case was introducedconventionally during the second stage of thermomechanical working, inorder to obtain the cross-linkable compositions F and G. The resultsobtained are set forth in Table 11 below:

TABLE 11 F G COMPOSITION E-SBR F E-SBR G ML (1 + 4) 100° C. rubber 45 49Properties in the non-vulcanized state ML (1 + 4) 100° C. 40 47Properties in the vulcanized state Shore A 64.1 62.1 ME10 (MPa) 4.804.39 ME100 (MPa) 1.37 1.56 ME300 (MPa) 1.48 1.79 ME300/ME100 1.08 1.15Scott break index at 20° C. BL (MPa) 21.1 20.1 EB (%) 642 569 Losses 60°C. (def. 40%) 37.6 35.4 Dynamic properties as a function of deformationΔG* 23° C. (MPa) 5.25 2.18 Tan (δ)_(max) 23° C. 0.420 0.319

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 of composition Gaccording to the invention (based on E-SBR G having acrylic acidfunctions along the chain) is greater than that of composition F (basedon non-functional E-SBR F) and, on the other hand, that the hysteresisproperties (losses at 60° C. and tan(δ) max at 23° C.) are improvedcompared with the hysteresis properties of composition F.

It would also appear that this composition G has a Mooney viscosity ofmix which is similar to that of composition F, that is to say aprocessing ability which is close to that of said composition F.

In other words, the elastomer E-SBR G, which comprises acrylic acidfunctions along the chain, makes it possible to obtain compositionshaving rubber properties in the cross-linked state which are improvedcompared with those of the “control” compositions based on anon-functional elastomer prepared in emulsion, and furthermore having aprocessing ability which is close to that of such “control”compositions.

(G) Seventh Comparative Example:

In this example, the properties of three rubber compositions F, G and G′of the “passenger-car”-tread type were compared with each other, thecompositions F and G having been defined in the preceding example andthe new composition G′ also being based on the elastomer E-SBR G havingacrylic acid functions along the chain. Composition G′ differed fromcomposition G only by the fact that all the ZnO is introduced into theinternal mixer during the first stage of thermomechanical working and ata temperature of 120° C. The results obtained are set forth in Table 12below:

TABLE 12 F G G′ COMPOSITION E-SBR F E-SBR G E-SBR G ML (1 + 4) 100° C.rubber 45 49 49 Properties in the non-vulcanized state ML (1 + 4) 100°C. 40 47 46 Properties in the vulcanized state Shore A 64.1 62.1 62.5ME10 (MPa) 4.80 4.39 4.17 ME100 (MPa) 1.37 1.56 1.46 ME300 (MPa) 1.481.79 1.69 ME300/ME100 1.08 1.15 1.15 Scott break index at 20° C. BL(MPa) 21.1 20.3 20.6 EB (%) 642 569 585 Losses 60° C. (def. 40%) 37.635.4 36.2 Dynamic properties as a function of deformation ΔG* 23° C.(MPa) 5.25 2.18 1.81 Tan (δ)_(max) 23° C. 0.420 0.319 0.301

As far as the properties in the cross-linked state are concerned, itwill be noted, on one hand, that the ratio ME300/ME100 of compositionG′, based on E-SBR G and with the addition of ZnO during the first stageof thermomechanical working, is greater than that of the “control”composition F and, on the other hand, that the hysteresis properties(losses at 60° C. and tan(δ) max at 23° C.) are greatly improvedcompared with the hysteresis properties of said composition F. Theseresults also show that composition G′ has hysteresis properties at lowdeformations which are improved compared with those of composition G.

Furthermore, it would appear that this composition G′ according to theinvention has a Mooney viscosity of mix which is substantially identicalto that of composition F (based on a non-functional elastomer preparedin emulsion). In other words, this composition G′″ has hysteresisproperties at low deformations which are improved compared with thoseobtained with the compositions F and G, and furthermore a processingability which is close to that of said “control” composition F.

(H) Eighth Comparative Example:

In this example, the properties of two rubber compositions H and I ofthe “passenger-car”-tread type were compared, composition H being basedon the non-functional E-SBR H and extended with the oil described inExample 1 (F) above and composition I being based on E-SBR I comprisingmethacrylic acid functions along the chain (see Example 1(G) above).

The formulation used for each of these compositions H and I was asfollows (in phr):

Elastomer extended with oil 127.5 Silica (1) 80 Aromatic oil “ENERFLEX65” 10 Bonding agent (2) 6.4 ZnO 2.5 Stearic acid 1.5 Antioxidant (3)1.9 Ozone wax “C32ST” 1.5 Sulfur 1.1 Sulfenamide (4) 2 Diphenylguanidine1.5 wherein: (1) = The silica ZEOSIL 1165 (RP); (2) = The bonding agentSi69 Dégussa; (3) = N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine;and (4) = N-cyclohexyl-2-benzothiazylsulfenamide.

Each of these compositions H, I was produced in the manner described inExample 2(F) above (in particular, with conventional introduction of theZnO during the second stage of thermomechanical working). The resultsobtained are set forth in Table 13 below:

TABLE 13 H I COMPOSITION E-SBR H E-SBR I ML (1 + 4) 100° C. rubber 50 48Properties in the non-vulcanized state ML (1 + 4) 100° C. 67 64Properties in the vulcanized state Shore A 67.2 68.7 ME10 (MPa) 6.446.76 ME100 (MPa) 1.72 2.09 ME300 (MPa) 1.95 2.37 ME300/ME100 1.13 1.13Scott break index at 20° C. BL (MPa) 24.8 23.1 EB (%) 590 519 Losses 60°C. (def. 40%) 34.0 33.0 Dynamic properties as a function of deformationΔG* 23° C. (MPa) 5.64 4.04 Tan (δ)_(max) at 23° C. 0.400 0.345

As far as the properties in the cross-linked state are concerned, itwill be noted that the hysteresis properties (losses at 60° C. andtan(δ) max at 23° C.) of composition I according to the invention (basedon an elastomer having methacrylic acid functions along the chain) areimproved compared with the hysteresis properties of the “control”composition H (based on a non-functional elastomer prepared inemulsion).

It would also appear that this composition I according to the inventionhas a Mooney viscosity of mix which is substantially identical to thatof the “control” composition H, that is to say a processing abilitywhich is close to that of said composition H. In other words, theelastomer E-SBR I makes it possible to obtain compositions having rubberproperties in the cross-linked state which are improved compared withthose of the “control” compositions based on a non-functional elastomerprepared in emulsion, and furthermore having a processing ability whichis close to that of such “control” compositions.

(I) Ninth Comparative Example:

In this example, the properties of three rubber compositions H, I and I′of the “passenger-car”-tread type were compared with each other, thecompositions H and I having been defined above and the new compositionI′ differing from composition I solely in that all the ZnO was addedduring the first stage of thermomechanical working. The results obtainedare set forth in Table 14 below:

TABLE 14 H I I′ COMPOSITION E-SBR H E-SBR I E-SBR I ML (1 + 4) 100° C.rubber 50 48 48 Properties in the non-vulcanized state ML (1 + 4) 100°C. 67 64 65 Properties in the vulcanized state Shore A 67.2 68.7 68.5ME10 (MPa) 6.44 6.76 6.49 ME100 (MPa) 1.72 2.09 2.02 ME300 (MPa) 1.952.37 2.29 ME300/ME100 1.13 1.13 1.13 Scott break index at 20° C. BL(MPa) 24.8 23.1 23.5 EB (%) 590 519 535 Losses 60° C. (def. 40%) 34.033.0 33.3 Dynamic properties as a function of deformation ΔG* 23° C.(MPa) 5.64 4.04 3.53 Tan (δ)_(max) 23° C. 0.400 0.345 0.341

As far as the properties in the cross-linked state are concerned, itwill be noted that the hysteresis properties (losses at 60° C. andtan(δ) max at 23° C.) of composition I′ according to the invention areimproved compared with the hysteresis properties of composition H. Theseresults also show that this composition I′ makes it possible to obtainhysteresis properties at low deformations which are improved comparedwith those of composition I.

Furthermore, it would appear that composition I′ has a Mooney viscosityof mix which is substantially identical to that of said “control”composition H based on a non-functional elastomer prepared in emulsion.In other words, composition I has hysteresis properties at lowdeformations which are improved compared with those obtained with thecompositions H and I, and it furthermore has a processing ability whichis close to that of said “control” composition H.

We claim:
 1. A cross-linkable or cross-linked rubber composition usableto constitute a tread for a tire, wherein said composition comprises:(a) a reinforcing filler comprising a reinforcing inorganic filler,wherein the mass fraction of said reinforcing inorganic filler in saidreinforcing filler is greater than 50%; and (b) at least one dieneelastomer having a molar ratio of units originating from conjugateddienes which is greater than 30% and comprising carboxylic acidfunctions along its chain, wherein said at least one diene elastomercomprising carboxylic acid functions along its chain is obtained, insolution, by: (i) subjecting the initial diene elascomer in an inerthydrocarbon solvent to a hydroalumination or carboalumination reactionalong its chain, by adding an agent derived from aluminum to saidinitial diene elastomer; (ii) adding to the product of saidhydroalumination or carboalumination reaction at least one electrophilicagent, wherein said electrophilic agent reacts with said agent derivedfrom aluminum; and (iii) stopping the reaction of said electrophilicagent and said agent derived from aluminum and recovering said at leastone diene elastomer comprising carboxylic acid functions along itschain.
 2. The cross-linkable or cross-linked rubber compositionaccording to claim 1, wherein said reinforcing inorganic fillercomprises a highly dispersible alumina.
 3. A. The cross-linkable orcross-linked rubber composition according to claim 1, wherein saidreinforcing inorganic filler comprises silica.
 4. The cross-linkable orcross-linked rubber composition according to claim 1, wherein saidreinforcing filler is present in said rubber composition in an amount ofequal to or greater than 40 parts by weight per hundred parts of dieneelastomer.
 5. The cross-linkable or cross-linked rubber compositionaccording to claim 1, wherein said composition comprises a reinforcinginorganic filler/diene elastomer coupling agent comprising a polysulfidealkoxysilane.
 6. The cross-linkable or cross-linked rubber compositionaccording to claim 5, wherein said polysulfide alkoxysilane isbis(3-triethoxysilylpropyl)tetrasulfide.
 7. The cross-linkable orcross-linked rubber composition according to claim 1, wherein saidrubber composition comprises a cross-linking system.
 8. Thecross-linkable or cross-linked rubber composition according to claim 7,wherein said cross-linking system is a sulfur-based system.
 9. Thecross-linkable or cross-linked rubber composition according to claim 1,wherein said at least one diene elastomer is selected from the groupconsisting of a homopolymer obtained by polymerization of a conjugateddiene monomer having from 4 to 12 carbon atoms and a copolymer obtainedby copolymerization of one or more dienes conjugated together or withone or more vinyl aromatic compounds having from 8 to 20 carbon atoms.10. The cross-linkable or cross-linked rubber composition according toclaim 1, wherein said at least one diene elastomer is selected from thegroup consisting of polybutadienes, butadiene/styrene copolymers andbutadiene/styrene/isoprene copolymers.
 11. The cross-linkable orcross-linked rubber composition according to claim 1, wherein said atleast one diene elastomer comprising carboxylic acid functions along itschain has a molecular weight exceeding 100,000 g/mol.
 12. Thecross-likable or cross-linked rubber composition according to claim 1,wherein said rubber composition comprises an elastomeric matrixcomprising in majority or formed by said at least one diene elastomercomprising carboxylic acid functions along its chain.
 13. A tread for atire comprising the cross-linkable or cross-linked rubber compositionaccording to claim
 1. 14. The tread according to claim 13 formed by saidcomposition.
 15. A tire comprising a tread according to claim
 13. 16. Atire comprising a tread according to claim 14.